The World Health Organization advises that no region in the world is justified in having a C-section rate >10- 15%. In 2004, the U.S. had a total rate of 29.1% and a primary rate of 20.6%. As these rates rise, so does the morbidity and mortality risk imposed on mothers and neonates. Dystocia is the greatest contributor to C- sections accounting for nearly 50% of all C-sections performed on nulliparous women. It is known that [1] abnormalities of uterine power are, by far, the greatest contributor to dystocia and [2] dystocia-afflicted labors that progress to a vaginal delivery have a much greater likelihood of increased labor lengths. This suggests uterine fatigue may be involved. This study will investigate factors that may: [1] contribute to increased labor length by increasing uterine fatigue; [2] indicate energy availability is inadequate; [3] indicate myometrial cell- damage has occurred. Specific aims will identify the relationships between labor length and maternal: [1] oxygen carrying capacity; [2] hydration status; [3] nutritive substrate status and; [4] myometrial cell-damage. A convenience sample of low-risk, nulliparous women in labor (n = 73) at term (> 37 - < 42 wks) will be studied. Identifying events / conditions that contribute to increased labor length via effects on uterine fatigue may unveil factors contributing to labor dystocia. Results may offer support to alternative labor management strategies.